Synthesis and structural characterization of binary PtNi alloy nanoparticles: investigating magnetic transition

Abstract

In this study, binary PtNi alloy nanoparticles were synthesized by one-pod reduction approach using modified polyol process with different atomic ratios of Pt and Ni. X-ray diffraction and Rietveld refinement analyses show well-defined single PtNi alloy formation of an fcc crystal structure with a space group of Fm$\overline{3 }$m. Increasing Pt content (from 0.25 to 0.75) in the PtNi alloy modified interatomic distance of Pt–Ni and increased the lattice constant from a = b = c = 0.3782 nm to a = b = c = 0.3834 nm and d₍₁₁₁₎-space from 2.18 to 2.22 Å. The average particle size was determined using a scanning electron microscope and found to be below 10 nm for all NPs. The composition-dependent magnetic properties of PtNi alloy NPs were investigated by vibrating sample magnetometer as a function of temperature between 5 and 300 K and magnetic field up to ± 3 T. Two distinct transition temperatures were observed that the first is superparamagnetic transition below 24 K and superparamagnetic-to-ferromagnetic transition below 125 K. Maximum coercive field is found to be 902 Oe for Pt_0.26Ni_0.74 NPs. However, hysteresis loops do not saturate up to ± 3 T and a maximum value of 8.54 emu/g is recorded for Pt_0.42Ni_0.58 NPs due to the small particle size of 7.82 ± 0.03 nm. The maximum value of K_eff is calculated as 2.61 $\times$ 10⁵ erg/cm³ for the 74% Ni sample due to the highest T_B = 24 K. The maximum μ_fu as 0.39μ_B and minimum as 0.09μ_B (Ni atom) were calculated for Pt_0.42Ni_0.58 and Pt_0.73Ni_0.27 NPs, respectively.